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#3708410 - 08/11/17 01:37 AM EATC Blower Motor Speed Controller Repair (Revised
Ponyguy Offline

Grand Poobah

Registered: 08/07/03
Posts: 12197
Loc: Oswego, IL
This is a revision to my original post from several years ago, outlining the repair procedure for a failed BMSC (Blower Motor Speed Controller) used with the EATC system on our Crown Vic LX's and GMQ LS models. (Probably on the Town Car, too, but I'm not certain.)

If there is no air blowing from anywhere on a car with EATC, one of the first things to suspect is the Blower Motor Speed Controller Module. The module is mounted on the heater/AC plenum in the engine compartment directly behind the passenger-side cam cover of the engine. A heater hose makes access difficult.

The factory modules are made in Mexico, and they are notorious for having a marginally-designed PC board layout along with poor soldering on the connections leading to the power transistor, which controls the current to the blower motor.

Here are some pictures I took of the Blower Motor Speed Controller from my GMQ... it failed a while back, and I took it apart and repaired it.

Here is the controller circuit board showing the faulty solder connection, directly below the third connector pin on top. The burned connection is readily visible:

Here is the circuit board after I resoldered the burned connection:

The circuit board foil adjacent to the connection was pretty thin and flimsy, so I reinforced the connection with some copper wire:

I re-installed the BMSC and it has performed flawlessly for well over four years now.
Sig removed. Read the rules.

So, I read the rules. Now I'm even more confused.

My transportation sources:
1972 Green Schwinn Speedster;
1984 Canyon Red Mustang V-6;
2004 Gold Ash GMQ LS Ultimate Edition, (Traded away, sadly);
2019 Turd Brown Fusion Titanium Hybrid Energie.

#3998298 - 12/14/18 10:45 AM Re: EATC Blower Motor Speed Controller Repair (Revised [Re: Ponyguy]
bspurloc Offline

Registered: 07/09/09
Posts: 887
Loc: New England
I did the same thing except at the connector where you see the etching flaked up I scraped off the top protector to fresh copper and layed down a huge solder blob to utilize all that area and cut down on resistance causing heat.
With yours you should have ran a wire thicker that that or doubled up cuz the circuit is pushing high amps and the heat from that is what causes that pin at the connector to desolder itself.
I posted pics of my fix but can't really search. NOw while on iPhone.
'03 Sport
'07 Audi Q7
'87 Thunderbird 250,000 miles v6 blown head gasket frown. I regret having it towed to the junk yard.

#4019420 - 06/24/19 10:55 PM Re: EATC Blower Motor Speed Controller Repair (Revised [Re: Ponyguy]
GoldPanther Offline
BOK contributor
Over the Hill

Registered: 07/16/13
Posts: 2908
Loc: Chitcagoland!
Thanks for the info ponyguy.

I was close to buy a new motorcraft module. You just saved me 90 bucks... 😁😁😁😁😀

Removing the module was easy even with a DOHC engine.

03 mgm ultimate edition.
June 2015 Panther of the Month
December 2018 Panther of the Month
Originally Posted By Black_Chrome
Black_Chrome: If only I had a merc...Oh wait, its still sitting out at the farm frown "This holiday season give that special woman in your life something she deserves. Dans External Relay Harness."

#4022574 - 07/14/19 06:59 PM Re: EATC Blower Motor Speed Controller Repair (Revised [Re: Ponyguy]
Stuntman Offline

Registered: 07/11/19
Posts: 20
Loc: Kansas
Nice fix.

On my '03, I had this module pop twice. Both times it was the transistor (the big metal can on the opposite side), that had burned up. Replacing the transistor required a little work, mostly to remount the heatsink, but was not excessive.
'03 Grand Marquis LS 217,000
'07 Grand Marquis LS, 100,000

#4022578 - 07/14/19 07:06 PM Re: EATC Blower Motor Speed Controller Repair (Revised [Re: Ponyguy]
RF_Overlord Offline


Registered: 12/14/02
Posts: 7676
Loc: MA
@Stuntman: The one in my '04 GMQ had the same problem as yours. I bought a Wells unit from Rock Auto but was looking to replace the transistor on the bad one and see if that actually fixes it.

Where did you obtain the transistor? (now that there's no more Radio Shack...)
'03 Mercury Marauder (The Blackbird)
Trilogy Motorsports supercharged #61
Too many mods to list / Driveway Queen

'04 Grand Marquis LS Limited Edition (Spruce Green)
Daily Driver (Thanks, Adam!)

'00 Grand Marquis GS (Silver)
Rotted frame and broken transmission crossmember
Being resurrected...slowly.

#4022588 - 07/14/19 07:56 PM Re: EATC Blower Motor Speed Controller Repair (Revised [Re: RF_Overlord]
Stuntman Offline

Registered: 07/11/19
Posts: 20
Loc: Kansas

From my records, the correct part number (in my case) was an MJ11028G from ON semiconductor. I would not be surprised if there were alternate part numbers used in these modules, but this is what was factory installed in mine. You can source this part from a lot of places:

They are around $15.

The process is not too bad if you know how to solder/desolder. The important highlights:

1. You will have to make provisions for holding down the heatsink after you remove it. I don't remember how it was from the factory, but I used two 4-40 screws and I seem to remember using little nylon sleeves to INSULATE the studs from the heatsink.

2. Use thermal compound or heatsink tape between the heatsink and the transistor CAN.

3. After the repair, I sprayed the solder side with conformal coating to protect the joints. Insulating varnish, or even spray paint would likely do the job just as well. May not even have to do it at all.

I make the process sound daunting. It did not take long. I modded mine after hearing horror stories about even the replacement blower modules frying immediately, or soon after replacement. So even if the cost was the same, it was worth it. Not to mention, when it blew a second time, the install and removal of the module was way more time than the transistor swap.

Feel free to PM me, or, if there is interest, I can give a better writeup on the forum.
'03 Grand Marquis LS 217,000
'07 Grand Marquis LS, 100,000

#4082702 - 10/31/20 11:35 PM Re: EATC Blower Motor Speed Controller Repair (Revised [Re: Ponyguy]
05silverbirch Offline

Registered: 10/15/16
Posts: 40
Loc: Michigan
so i have a 05 grand marquis. and just started to happen. where i have blower working on HI but nothing on low or medium. this happens on and off. i could just have the knob set in the middle and the blower would start working again. is my resistor going bad... or is bad and its a hit and miss with the connection.


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